1. Technical Field
This invention generally relates to musical apparatus. In particular the invention pertains to an apparatus for determining a tonality from a chord progression and to an automatic accompaniment performing apparatus.
2. Description of Prior Art
An electronic musical instrument having an automatic accompaniment performing capability is known. A play input device (e.g., musical keyboard) of the musical instrument is used to successively designate chords each represented by a keycode (note number) combination to provide a chord progression. Within the musical instrument there is provided a chord member memory which stores members of each chord in a chord set. Each stored chord member indicates a pitch interval from a chord root. Assuming that one of a plurality of keycodes (note numbers) entered from the keyboard is a root of the chord designated by the plurality of keycodes, a chord root and type determining means converts each entered keycode to a corresponding pitch interval from that root to obtain designated chord member data comparable with that of the chord member memory. The chord root and type determining means identifies a type and root of a designated chord by finding stored chord member data of a particular chord type that matches the designated chord member data. In this manner, there is formed a chord progression in which each chord is represented by a root and a type. The musical instrument further includes an accompaniment pattern memory storing an accompaniment pattern. The accompaniment pattern comprises horizontal (time) component and vertical (pitch) component of an accompaniment line. An accompaniment decoding means converts the stored vertical data to pitch data indicative of an actual pitch of the accompaniment in accordance with an identified chord type and root.
The musical instrument described above has no capability of evaluating a function of a chord in a chord progression. In general, in music, even if a type and root of a chord is known, this is not enough to determine a tonality i.e., a pitch class set available in the time interval of that chord. By way of example, take up a chord of C major (root=C, type=major) having members of C, E and G. If C major chord has a function of tonic (I), a desired set of pitch classes are C, D, E, F, G, A and B which form an ionian scale in a key of C. If the same chord has a function of dominant (V), a set of pitch classes C, D, E, F, G, A and B.music-flat. forming a mixolydian scale in key F may be suitable. In the case when C major chord has a function of subdominant (IV), a desired set of pitch classes will be C, D, E, F.music-sharp., G, A and B which form a lydian scale in key G. As noted, it is a nature of music that a specified function as well as specified type and root of a chord is required to determine a desired pitch class set (tonality). Nevertheless, this is disregarded in the musical instrument stated above which instead decodes the stored accompaniment pattern by using only a chord root and type to determine accompaniment pitches. The resultant accompaniment can sound unnatural because of undesirable pitches contained therein that weaken or damage the desired tonality. This may be avoided by restricting vertical contents of the accompaniment to, for example, chord member pitches only. This solution, however, will deprive the accompaniment of musical interest because of its poor pitch contents.
U.S. Pat. No. 5,003,860, issued Apr. 2, 1991 and assigned to the same assignee as the present application discloses a tonality determining apparatus which determines a tonality from a chord progression and an automatic accompaniment performing apparatus which uses the results from the tonality determining means to play an accompaniment. This tonality determining apparatus uses algorithms (programs) rather than data to realize musical knowledge required for determining a tonality. Because of its principles, the tonality determining apparatus provides a tonality with a relatively low reliability. In other words, to obtain an accurate tonality, the tonality determining apparatus of this type would require complicated logic and arithmetic operations consuming a considerable time which would not be permissible in real-time applications such as automatic accompaniment performing apparatus.
Another example of tonality determining apparatus and automatic accompaniment performing apparatus is disclosed in Japanese patent application laid open to public as Kokai Hei2-29787. This tonality determining apparatus searches from a given chord progression for a portion indicative of a specific chord pattern having a particular chord type pattern and a particular chord root difference pattern to determine a key. However, the tonality determining apparatus will never use or reference a key determined already for a preceding portion of the chord progression to determine a key for a succeeding chord in the chord progression. This tends to introduce a delay in detecting a modulation (change of key), resulting in wrong key determination for a portion of the chord progression. Thus, an automatic accompaniment performing apparatus, which is an application of such tonality determining apparatus, cannot hope to perform a satisfactory accompaniment for the reasons stated before.
U.S. patent application Ser. No. 07/681,085 filed Apr. 5, 1991, issued on Jan. 12, 1993 as U.S. Pat. No. 5,179,241 and assigned to the same assignee as the present application discloses a tonality determining apparatus which determines a key of a succeeding chord by using a prevailing key as clue. This tonality determining apparatus has a same key function for determining whether a succeeding chord keeps the prevailing key and a modulation detecting function for determining whether a succeeding chord suggests a key related to the prevailing key. Thus, the tonality apparatus can provide a relatively correct recognition of a key of each chord in a chord progression, and detect a modulation to a closedly related key without delay. Yet, in real music, there are various situations all of which the apparatus cannot successfully handle. In actual music, for example, a succeeding key can be unrelated to a preceding key. A beginning portion of a music piece has no preceding key. A preceding or prevailing key can be unspecific or indefinite. These regions of music phenomena are beyond the capability of the tonality determining apparatus which, thus, leaves room for improvement.
The above U.S. Pat. No. 5,179,241 also discloses an automatic accompaniment apparatus which plays an automatic accompaniment by utilizing results (chord function, type and key) from a real-time tonality determining means. The resultant accompaniment has a relatively natural tonality.
However, the accompaniment forming device of the automatic accompaniment apparatus is arranged such that it first forms an accompaniment pattern written in a particular key and then "transposes" it according to a key supplied from the tonality determining apparatus. This gives rise to a pitch-leaping problem in connection with a modulation (change of key). The pitch or range of a played accompaniment line changes or shifts between before and after the modulation to an extent corresponding to the difference between the key before the modulation and the one after the modulation. This is called a leap motion in pitch line.
Such a leap motion phenomenon is undesirable except when the music of interest has such an intention. Users (listeners) of the apparatus would feel unnaturalness.
The same problem is involved in the automatic accompaniment apparatus disclosed in U.S. Pat. No. 5,003,860 and Japanese patent application laid open Hei2-29787.
Whereas the apparatus disclosed in U.S. Pat. No. 5,179,241 can provide an accompaniment with a natural tonality, it still has the limit in its tonality determining capability since musical (tonality) information derivable from a chord progression only is limited due to a nature of music. In fact, a pitch class set suitable in each chord time interval in a given chord progression depends not only on the chord function but also relies on a particular musical style to which an intended accompaniment is directed. As stated the prior art automatic accompaniment apparatus has two distinct types. The first type forms an accompaniment based on a chord root and a chord type. The second type apparatus forms an accompaniment based on a chord tonality (i.e., keynote, function and type). The automatic accompaniment apparatus of the first type provides an accompaniment with undesirable pitches whereas the apparatus of the second type provides a relatively natural accompaniment although it requires means for analyzing a chord progression for extraction of tonality.
An important problem of the accompaniment formation is to provide a natural and real accompaniment while saving the storage capacity required for the accompaniment data. Unfortunately, no prior art automatic accompaniment apparatus has successfully solved this problem.
For example, a prior art chord root/type based automatic accompaniment has a stored accompaniment pattern suited for a reference chord root and type, corrects pitch data in the stored accompaniment pattern according to a detected chord type, and adds a detected chord root to the corrected pitch data. Whereas this arrangement requires only a small amount of storage capacity, it provides an unnatural accompaniment with undesirable pitches. A known tonality based automatic accompaniment apparatus includes a memory storing a large number of accompaniment patterns grouped by accompaniment styles and tonalities and selects, when operated, a particular accompaniment pattern corresponding to a combination of a designated accompaniment style and a recognized tonality. Though it can provide a real accompaniment with a variety, this arrangement requires an enormous amount of storage and is unfeasible when implementing on a single or few chip microcomputer.